Moth sex pheromone adsorption to leaf surface: bridge in time for chemical spies

Abstract When brussels sprouts leaves were exposed to air passed over a single calling Mamestra brassicae moth, sex pheromone was adsorbed onto the leaf surface to such an extent that it subsequently elicited behavioural responses in conspecific male moths, as well as in female Trichogramma evanescens , egg parasitoids of M. brassicae. Male moths responded to odour-treated leaves over a short distance (c. 5 cm) in a wind tunnel, but were not attracted at a distance of 1 m. In contrast, sex pheromone adsorbed to and re-released from the glass wall of a wind tunnel compartment attracted male moths from 1 m. Trichogramma's locomotory behaviour on leaves is described. On leaves previously exposed to air passed over a calling female moth, Trichogramma wasps stayed significantly longer on leaves treated with clean air or air passed over a non-calling female moth. In addition, wasps spent relatively more time along the margin and on the leaf underside on treated leaves compared with control leaves. All effects persisted for at least 4 h, and after 24 h treated leaves still increased wasp residence times. These results are the first example of responses of male moths to adsorbed airborne sex pheromone originating from a single female moth. They further suggest how sex pheromone released by nocturnal moths may function as a kairomone for diurnally foraging parasitoids.